This invention relates to a recording meduim for recording with an ink and, more particularly, to an ink jet recording medium which provides images or letters of high density and of superior water resistance and light resistance.
Ink jet recording system performs recording of images or letters by squirting fine drops of ink by various actuation principles onto recording media such as paper. These ink jet recording systems have characteristics such as high-speed and low-noise recording, easy multicolor recording, great versatility of recording patterns and do not require development and fixation. Such systems rapidly becoming popular in various uses such in recording devices for various figures including Chinese characters and color images. Furthermore, multicolor ink jet recording systems can provide images which are by no means inferior to those obtained by multicolor printing with printing plates or by color photographic methods and thus, because of these systems are less expensive than photographic method, ink jet systems are increasingly being employed even in the fields of fullcolor image recording if many prints are not required.
In an attempt to use wood free papers or coated papers as used in ordinary printing or writing, as a medium for ink jet systems, efforts are focused on improving devices and composition of ink. However, with improvements in performances of ink jet recording devices such as recording speed and precision of recorded images and with enlargement of uses such as full coloration of images, new recording medium is also required to posses improved characteristics, for example, as follows: It should provide ink dots of high density and clear and bright color; It should rapidly absorb ink, causing neither flowing nor blotting of ink when ink dots overlap; Ink dots should not unnecessarily spread in a planar direction and the periphery of the dots should be smooth and unblurred. Furthermore, it is required that when recorded images are exposed to unltraviolet rays, oxygen or water, dye resistance should not decrease and preferably is enhanced.
Some proposals have been made to solve these problems. For example, Japanese Patent Application Kokai (Laid-Open) No. 52-53012 discloses an ink jet recording paper which comprises a raw paper of low size content which is wetted with a surface finishing coating composition. Japanese Pat. application Kokai (Laid-Open) No. 53-49113 discloses an ink jet recording paper which comprises a paper containing urea-formalin resin powders impregnated with a water-soluble polymer. These ink jet recording papers of plain paper type have rapid ink absorbing properties, but still suffer from the defects in that the periphery of ink dot tends to be blurred and the density of dot is low.
Further, Japanses Patent Application Kokai (Laid-Open) No. 55-5830 discloses an ink jet recording paper comprising a support provided with an ink absorbing coating layer on the surface; Japanese Patent Application Kokai (Laid-Open) No. 55-51583 discloses an example of using non-colloidal silica powder as pigment in the coating layer; Japanese Patent Application Kokai (Laid-Open) No. 55-11829 discloses a paper coated with two layers having different ink absorbing rates and especially Japanese Patent Application (Laid-Open) Nos. 59-174381, 60-44386, 60-132785 and 60-171143 disclose ink jet recording papers provided with transparent ink receiving layers. These ink jet recording media of coated type are superior substrates relative to ink jet recording papers of plain paper type in providing dots of better diameter and shape, image density and reproducibility of color tone, but these substrates are also defective in that aqueous ink containing water-soluble dye is often used for them and if an image formed on the media is splashed with water, the dye redissolved and diffuses, resulting in a considerable reduction of the value of the record. The dye is severely deteriorated due to high light transmittance and gas permeability of the ink receiving layer.
Improving the water resistance has been proposed as follows: The application water-soluble salts of metal to the recording surface (Japanese Patent Application Kokai (Laid-Open) No. 55-53591); a recording medium containing a polycationic high polymer electrolyte in the surface (Japanese Patent Application Kokai (Laid-Open) No. 56-84992); use of a water resistant agent which forms a lake with the dye in the ink after ink jet recording (Japanese Patent Application Kokai (Laid-Open) No. 55-150396); a method of rendering the images ink-jet recorded on a recording sheet, water resistant by coating with water-soluble polymer by insolubilizing said water-soluble polymer (Japanese Patent Application Kokai (Laid-Open) No. 56-58869); Insolubilization of the dye with a halogenated quaternary ammonium or salt of alkylammonium (Japanese Patent Application Kokai (Laid-Open) Nos. 56-99693 and 59-96987); Converting dye to lake with water-soluble salts of metals (Japanese Patent Application Kokai (Laid-Open) No. 59-96988).
However, these methods, are not totally effective in rendering images water resistant. Additional water resistant agents cause some reactions with the dye, resulting in considerable reduction in stability of dye, and as a result it is difficult to obtain well-balanced quality as recording medium.
On the other hand, in order to improve light resistance of recorded images, Japanese Patent Application Kokai (Laid-Open) Nos. 54-68303, 54-85804 and 56-18151 propose addition of ultraviolet absorbers to ink solution. However, these ultraviolet absorbers cause reduction of the jetting stability of ink and cannot be added in a large amount because of their low solubility. Small additions provide only a small effect. Another solution, relates to the addition of ultraviolet absorbers such as benzophenone and benzotriazole compounds to an ink jet recording sheet as disclosed in Japanese Patent Application Kokai (Laid-Open) Nos. 57-74192, 57-74193 and 57-87988. However, these ultraviolet absorbers have problems in that their solubility in water is low and cannot be used in a large amounts. The addition of small amounts cannot provide sufficient effect and if they are emulsified, the emulsion gives adverse results. Still another is disclosed in, Japanese Patent Application Kokai (Laid-Open) Nos. 61-43593 and 61-47290 which propose the addition of metal slats such as weak acid salts of alkali metals. However, when these are used in large amounts, the color quality of images is deteriorated and when used in a small amount, the effect is small.
Furthermore, due to the problem that use of a water resistant agent in combination with ultraviolet absorber damages effects, it has been very difficult to obtain recording media which can provide images balanced in quality and having high color quality, water resistance and light resistance and superior ink absorbability.